Formation, production and viability of oospores of Phytophthora infestans from potato and Solanum demissum in the Toluca Valley, central Mexico

Aspects of the ecology of oospores of Phytophthora infestans were studied in the highlands of central Mexico. From an investigation of a random sample of strains, it was found that isolates differed in their average capability to form oospores when engaged in compatible pairings. Most crosses produced large numbers of oospores but a few yielded none and some yielded only a few oospores. The results reveal that oospore production and fecundity is dependent on both isolates and the combining ability of a specific combination of parental strains. On average, 14% of the oospores produced were viable as determined by the plasmolysis method. Viability ranged from a low 1% in one cross to a high of 29% in another cross. Oospores were found in 10-20% of naturally infected Solanum demissum leaves from two different collections, and leaflets with two lesions per leaflet produced more oospores than did leaflets with 3-5 lesions per leaflet. There was no consistent trend for preferential mating between isolates from the same location or host

Structurele en tijdelijke tekorten van micro- en macro-elementen bij de zetmeelaardappelteelt in Noordoost-Nederland

Onderzoek naar de aanwezigheid en aard van gebrekverschijnselen bij de zetmeelaardappelteelt in Noordoost-Nederland hebben het volgende beeld opgeleverd. Uit surveys te velde bleek dat symptomen samenhangend met gebrek aan calcium en borium bij kiemende en uitlopende gewassen veel voorkomen. Uit de waarnemingen aan tijdens de surveys verzameld materiaal komt naar voren dat voor calcium en borium ernstige tekorten in pootaardappels en moederknollen voorkomen

Partial resistance of tomatoes against Phytophthora infestans, the late blight fungus

In the Netherlands, the source of inoculum of the late blight fungus on tomatoes is the late blight fungus on potato crops. In regions of Europe mentioned, where tomatoes are grown in the open, P. infestans on tomatoes is the main source of inoculum. Especially in Bulgaria and Hungary, the effect of year-round cropping of tomatoes on prevalence and severity of the disease is obvious.In field and laboratory experiments, the pathogenicity to tomatoes of P. infestans originating from potatoes can be increased by serial passages through tomato foliage. In Europe, no other hosts than potatoes and tomatoes played a role in the tomato late blight epidemidogy. Phacelia tanacetifolia is added to the host list of the fungus. For the purpose of genetics classification, two laboratory methods, probit - log dosage analysis and components analysis, and one field method have been developed to assess the resistance of tomatoes against P.infestans.In particular the components infection ratio, lesion extension and sporulation intensity were studied. In the field method, the 'apparent infection rate' r was used. For breeding purposes, a simplified field method was indicated. A comparison of the three methods was made.The resistance of tomatoes increased considerably until at least 8 weeks after seeding. Partial resistance of W.Va 700 against the 1-t-pathotype of P.infestans is based on a single gene, here named Ph 2

Mogelijkheden en vooruitzichten voor de beheersing van bodemgebonden ziekten van de aardappel met groenrooien = Possibilities and prospects for the control of soil - related diseases of the potato by green - crop - harvesting

Het groenrooien wordt toegepast om besmetting van de knol met lakschurft te voorkomen.De methode en het effect daarvan worden beschreve

Mating type, mefenoxam sensitivity, and pathotype diversity in Phytophthora infestans isolates from tomato in Brazil

The objective of this work was to characterize 79 Phytophthora infestans isolates collected in tomato (Solanum lycopersicum) fields, as to mating type, mefenoxam sensitivity, and pathotype composition. The isolates were sampled in 2006 and 2007 in seven Brazilian states as well as in the Distrito Federal. They were characterised as to mating type (n=79), sensitivity to fungicide mefenoxam (n=79), and virulence to three major resistance genes Ph-1, Ph-2, and Ph-3/Ph-4 (n=62). All isolates were of the mating type A1. Resistant isolates were detected in all sampled states, and its average frequency was superior to 50%. No difference was detected in pathotype diversity, neither between subpopulations collected in 2006 and 2007 nor between isolates grouped as resistant or intermediately sensitive to mefenoxam. All major resistance genes were overcome at different frequencies: Ph-1, 88.7%; Ph-2, 64.5%; and Ph-3/Ph-4, 25.8%. Isolates with virulence genes able to overcome all major resistance genes were detected at low frequencies. Tomato breeding programs in Brazil must avoid the development of cultivars with resistance based exclusively on major genes